But there was no mention of the president. Nor any mention of health care, aside from a reference to Cuccinelli's participation, as Virginia attorney general, in conservative efforts to restrict women's health care (read abortion rights) in the state. It was noticed.

Biden's omission signaled how the Affordable Care Act's recent troubles have turned the president's signature domestic legislation from an asset to a liability, if not in solidly blue places like Massachusetts then in purple states like Virginia.

At a rally in Virginia a day before Biden's appearance, Obama didn't mention Obamacare, either. He did mention Biden, however.

The vice president's omission may have also signaled something else. In their new book about last year's presidential campaign, Double Down: Game Change 2012, due out Tuesday, journalists Mark Halperin and John Heilemann reported that Obama campaign aides considered dropping Biden from the ticket in favor of then-Secretary of State Hillary Clinton. Veteran Obama political strategists like David Axelrod and David Plouffe have denied Biden was ever at risk of being jettisoned.

It's possible to read too much into such moments, of course. But sometimes a politician says more by what he doesn't say than by what he does.